Bloom has argued that most students, not just a few, should be able to do top quality school work if given appropriate instruction. Mastery learning, which includes frequent diagnostic testing followed by remedial instruction, has been proposed as an effective strategy for increasing pupil achievement. In this study, teachers used a mastery learning strategy with elementary school students in a geometry unit. An analysis of the data indicated that low mathematics aptitude fourth graders taught using a mastery strategy achieved at as high a level as high aptitude fifth graders taught in a more conventional manner. (Author)